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The Digestive Tract (Digestion Process (Chemical digestion (By secreted…
The Digestive Tract
Digestion Process
Chemical digestion
By secreted enzymes of carbs, lipids etc
Absorption
Transport of digested end products into blood and lymph in wall of canal
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation
Defecation
Elimination indigestible substances as feces
Propulsion
Swallowing
Peristalsis - propulsion by alternate contraction and relaxation
Ingestion
Taking food through mouth
Teeth
Incisors: chisel-shaped for chopping off pieces
Canines: Cone shaped to tear and pierce
Premolars: (Bicuspids) and
Molars: broad crowns with 4-5 rounded cups for grinding
Two main regions
Crown (exposed)
Root (in socket)
Meet at neck
Enamel
99% calcium crystals
Hardest substance in body
Dentin
Bulk of tooth (bone-like but harder than boone, with collagen and mineral)
Pulp cavity with vessels and nerves
Root canal: part of pulp in the root
Cementum
: bone layer of tooth root
Attaches tooth to periodontal ligament
Periodontal ligament
Anchors tooth in boney socket of jaw
Continuous with gingiva (gums)
cavities/caries
: rot
Plaque
: film of sugar, bacteria and debris
GI tract
Muscular alimentary canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Accessory digestive organs
Supply secretions contributing to breakdown of food
Teeth & tongue
Salivary glands
Gallbladder
Liver
Pancreas
Smooth Muscle
Muscles spindle shaped cells
One central nucleus
Grouped into sheets: often running perpendicular to each other
Peristalsis
No striations (no sarcomeres)
Contractions are slow, sustained and resistant to fatigue
Does not always require nervous signal: can be stimulated by stretching or homes
Locations
Inside eye
Walls of vessels
Respiratory tubes
digestive tubes
Urinary organs
Reproductive organs
Nerves
Autonomic input:; speeds up/slow down digest
Parasympatheitc
Stimulates digestive functions
Sympathetic
Inhibits digestion
Largely automatic
Enteric nervous system
visceral plexuses within gut wall controlling muscles, glands and having sensory info
Mesenteries
Dorsal (posterior) mesenteries
Greater omentum
connects stomach to posterior abdominal wall
Lot of fat
Mesentery proper
Supports jejunum and ileum
Transverse mesocolon
Transverse colon held to posterior abdominal wall
Nearly horizontal sheet fused to underside of greater imentum
Sigmoid mesocolon
Connects sigmoid colon to posterior abdominal wall
Two ventral mesenteries
Falciform 'ligament'
Binds anterior aspect of liver to anterior abdominal wall and diaphragm
Lesser omentum (fatty skin)
Mouth
Oral cavity
Lining: thick stratified squamous epithelium
Lips: orbicularis oris muscle
Cheeks: buccinator muscle
Vermilion border/red border
Between highly keratinized skin of face and mucosa of mouth
Needs moisture
Note frenulums (folds of mouth)
Palate (roof of mouth)
Hard palate anteriorly
Soft palate posteriorly
Uvula
Salivary glands
Intrinsic salivary glands
: within mucosa
Secrete saliva all the time to keep mouth moist
Extrinsic salivary glands
Paried (2 each)
Parotid
Submandibular
Sublingual
External to mouth
Ducts to mouth
Secrete saliva only right before or during eating
Saliva
Mixture of water, ions, mucus, enzymes
Keep mouth moist
Dissolves food so can be tasted
Moistens food
Starts enzymatic digestion
Buffers acid
Antibacterial and antiviral
Histology alimentary canal wall
-
Submucosa
Connective tissue containing major blood and lymphatic vessels and nerves
Many elastic fibers so gut can regain shape after food passes
Muscularis externa
Longitudinal muscle: outer, shortens gut
Circular muscle: squeezes, in some places forms sphincters (act as valves)
Mucosa
Epithelium: absorbs nutrients, secretes mucus
Continous with ducts and secretory cells of intrinsic digestive glands (those within the wall)
Lamina propria
Loose connective tissue with nourishing and absorbing capillaries
Contains most of mucosa-associated lymphoid tissue (MALT)
Muscularis mucosae
Thin layer muscle producing only local movements
Serosa
Simple squamous Epithelium (mesohelium)
Thin layer of areolar connective tissue underneath
Lymphoid tissue
Defintions
Peritoneum
: serous membranes of abdominopelvic cavity
Visceral peritoneum
: Covers external surfaces most digestive organs
Parietal peritoneum
: lines body wall
Peritoneal cavity: Slit-like potential space between visceral and parietal peritoneum
Serous fluid - lubricating
Tongue
Mostly muscles
Grip and reposition food
Forms bolus of food
Helps in swallowing
Speech
Taste buds contained by circumvallate and fungiform papillae
Lingual tonsil - back of tongue
Arteries of GI tract :red_cross: